Testing fuse configurations in semiconductor devices

ABSTRACT

Methods, systems, and apparatus for testing semiconductor devices. A semiconductor device includes one or more external terminals configured to receive fuse configuration data from an external source. The semiconductor device also includes a soft-blow circuit to generate a soft-blow signal based on the fuse configuration data, and a fuse circuit that includes a fuse and has first and second operational states corresponding to the fuse being intact and blown, respectively. The fuse circuit is configured to receive the soft-blow signal and to select its operational state to be the first or second operational state based on the received soft-blow signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending application Ser. No.12/008,318, filed on Jan. 10, 2008, which is a continuation in part ofapplication Ser. No. 11/472,016, filed on Jun. 20, 2006, now U.S. Pat.No. 7,466,160, which is a continuation in part of application Ser. No.11/207,665, filed on Aug. 18, 2005, now U.S. Pat. No. 7,309,999, whichis a continuation in part of application Ser. No. 11/108,385, filed onApr. 18, 2005, now U.S. Pat. No. 7,259,582, which is a division ofapplication Ser. No. 10/608,613, filed on Jun. 27, 2003, now U.S. Pat.No. 6,882,171, which is a continuation in part of application Ser. No.10/305,635, filed on Nov. 27, 2002, now U.S. Pat. No. 6,812,726. Thedisclosures of all the above patents and patent applications are herebyincorporated by reference.

BACKGROUND

The present invention relates to semiconductor devices, and inparticular, testing fuse configurations in semiconductor devices.

A semiconductor device includes one or more integrated circuit (IC)devices, each of which includes many miniaturized circuits implementedin a single semiconductor substrate, commonly referred to as a “chip.”The IC devices are typically tested before they are used in order toensure their proper operation. The IC devices can be tested in a limitedfashion using built-in self test (BIST) circuitry that is implementedwithin the IC devices themselves. BIST testing however, is oftenincomplete and does not test all aspects of the device operation.Thorough testing of an IC device is traditionally accomplished withcomplex external testing equipment that typically requires manydedicated input/output (I/O) leads for allowing the test equipment toinput various test patterns, codes, and data, and to stress thecircuitry of the IC device. The use of the external testing equipmentcan be particularly difficult if multiple IC devices are combined withina single package that has a limited number of input/output leads, and athorough test is required for one or more of the devices within thepackage.

Some IC devices include fuses that can be selectively and permanently“blown,” for example, by laser to optimize or fine tune certain electricor other operational parameters of particular device elements such asvoltage regulators or delay elements. To find the optimal values ofthose electric or other operational parameters, such IC devices aretraditionally tested for multiple fuse configurations in which differentfuses are blown. Because the fuses are permanently blown in each of thedifferent configurations, the traditional test requires different ICdevices to implement different fuse configurations.

SUMMARY

An IC device includes one or more fuses and, for each fuse, a respective“soft-blow” circuit that can be programmed to simulate electricconditions in which the corresponding fuse is blown. By appropriatelyprogramming the soft-blow circuits, multiple fuse configurations can betested in the same IC device without permanently blowing any of thefuses. Once the optimal fuse configuration has been found, thecorresponding fuses can be permanently blown, for example, by laser.

In general, in one aspect, the present invention provides asemiconductor device that includes one or more external terminalsconfigured to receive fuse configuration data from an external source.The semiconductor device also includes a soft-blow circuit to generate asoft-blow signal based on the fuse configuration data, and a fusecircuit that includes a fuse and has first and second operational statescorresponding to the fuse being intact and blown, respectively. The fusecircuit is configured to receive the soft-blow signal and to select itsoperational state to be the first or second operational state based onthe received soft-blow signal.

Particular implementations can include one or more of the followingfeatures. The soft-blow circuit can include a latch to receive and holda portion of the fuse configuration data. The semiconductor device canalso include one or more external terminals that are configured toreceive mode selection signals to select between a test mode and anormal mode of operation for the device. Generating the soft-blow signalcan be enabled in the test mode and disabled in the normal mode.Receiving the fuse configuration data can be disabled in the normalmode. The mode selection signals can define a programming phase of thetest mode, and receiving the fuse configuration data can be enabled onlyduring the programming phase. The soft-blow circuit can receive a dataenable signal that enables receiving the fuse configuration data. Thefuse circuit can generate an output signal that is different in thefirst operational state from that in the second operational state. Thesemiconductor device can also include a voltage generator coupled to thefuse circuit to generate a reference voltage that is different in thefirst operational state of the fuse circuit from that in the secondoperational state. Alternatively or in addition, the semiconductordevice can include a delay element coupled to the fuse circuit andconfigured to receive an input signal and to output a delayed signalfollowing the input signal by a time delay that is different in thefirst operational state of the fuse circuit from that in the secondoperational state. The fuse circuit can be configured (i) to generate aninternal fuse signal based on the fuse being intact or blown, (ii) tocombine the internal fuse signal and the received soft-blow signal, and(iii) to select its operational state to be the first or secondoperational state based on the combined signal. The fuse circuit caninclude one or more additional fuses and have additional operationalstates that correspond to one or more of the additional fuses beingblown, and wherein the soft-blow circuit generates one or moreadditional soft-blow signals based on the fuse configuration data, andwherein the fuse circuit is configured to select its operational stateto be one of the additional operational states based on the additionalsoft-blow signals. The soft-blow circuit can receive the fuseconfiguration data on parallel data lines, and each data line cancorrespond to a respective fuse in the fuse circuit. Or, the soft-blowcircuit can receive the fuse configuration data for two or more fusesusing a serial communication line.

In general, in another aspect, the present invention provides anintegrated circuit device packaged in a semiconductor device package.The integrated circuit device includes one or more external terminalsconfigured to receive mode selection signals selecting between a testmode and a normal mode of operation for the device, and one or moreexternal terminals configured in the test mode to receive fuseconfiguration data from an external source. The device also includes alatch array and a fuse array circuit. The latch array includes aplurality of latches each of which being configured in the test mode toreceive a corresponding data portion of the fuse configuration data andto output a respective soft-blow signal based on the received dataportion. The fuse array circuit includes a plurality of fuses andgenerates a respective output signal for each fuse based on whether thatfuse is blown or not, wherein each latch in the latch array correspondsto a respective fuse in the fuse array circuits, and in the test modethe fuse array circuit receives the respective soft-blow signal fromeach latch and generates the respective output signal for that fusebased on the received soft-blow signal.

Particular implementations can include one or more of the followingfeatures. The device can include a circuit element that receives one ormore of the output signals from the fuse array circuit and selects itsoperational state based on the received output signals. The circuitelement can include a voltage regulator providing a reference voltagewhose value depends on the output signals from the fuse array circuit.Or the circuit element can include a delay element configured to receivean input signal and to output a delayed signal following the inputsignal by a time delay whose value depends on the output signals fromthe fuse array circuit.

In general, in yet another aspect, the present invention provides amethod for operating a semiconductor device in a semiconductor devicepackage. The method includes receiving fuse configuration data from anexternal source, generating a soft-blow signal based on the receivedfuse configuration data, receiving the soft-blow signal in a fusecircuit that includes a fuse and has first and second operational statescorresponding to the fuse being intact and blown, respectively, andselecting the fuse circuit's operational state to be the first or secondoperational state based on the received soft-blow signal.

Particular implementations can include one or more of the followingfeatures. The method can include generating a tune signal in accordancewith the fuse circuit's operational state, and transmitting the tunesignal to a circuit element to tune operational parameters of thatcircuit element, wherein the circuit element can include a voltageregulator or a signal delay element.

In general, in yet another aspect, the present invention provides amethod for testing semiconductor devices. The method includes putting asemiconductor device into a test mode, wherein the semiconductor deviceincludes a set of fuses, and testing the semiconductor device for aplurality of fuse configurations without permanently blowing the fuses,wherein each fuse configuration corresponds to a respective subset ofblown fuses within the set of fuses.

Particular implementations can include one or more of the followingfeatures. Testing the semiconductor device for a plurality of fuseconfigurations can include, for each fuse configuration, loading fuseconfiguration data into a soft-blow circuit of the semiconductor device,wherein the fuse configuration data defines the respective subset ofblown fuses within the set of fuses. Operational parameters can bemeasured in each fuse configuration, and an optimal fuse configurationcan be determined based on the measured operational parameters.

Particular embodiments can be implemented to realize one or more of thefollowing advantages. An IC device can include soft-blow circuits thatcan be programmed to test a large number of different fuseconfigurations. Thus, an optimal fuse configuration can be found withoutpermanently blowing the fuses. The optimal fuse configuration can befound without using and, after the test, discarding many IC devices.Using a single IC device for the test can also decrease inaccuraciesresulting from the potentially different set-up for the many IC devices.A software program can test many different (potentially all)combinations and permutations of “blown” fuses on a single die in oneprobe touch down. Based on the test results, the appropriate fuseconfiguration can be selected to obtain a desired result. Such “softblow” tests eliminate the need of physically blowing each fuse on a dieand using multiple dice for the different fuse configurations. The“soft-blow” techniques can be used to characterize differentcombinations and permutations of the fuse configurations on each diethat is from the same wafer but at different locations on that wafer;thus one can record or study deviations from the optimal “uniformess” ofthe wafer process. Based on such deviation record, the actual fuses canbe blown selectively based on their location on the wafer to giveuniform results for each die on the wafer. Thus, each die can beadjusted to behave substantially the same way (e.g., to achieve uniformvoltage outputs or timing specifications) by adjusting internal voltagelevels and delay elements.

The soft-fuse techniques can also be used to adjust setup and holdtimes, timing skews, jitter (e.g., in DLL circuits), output drivestrengths, oscillator frequencies (e.g., to control self-refreshperiod), voltage biasing and regulation circuits. The soft-fusetechniques can be implemented “on the fly” during production. Suchon-the-fly soft-fuse testing can be implemented with relatively smallimpact to the through-put of the production. Further technicaladvantages are readily apparent to one skilled in the art from thefollowing figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic block diagrams illustrating exemplarysemiconductor devices in which the present invention can be implemented.

FIGS. 2A-2C are schematic block diagrams illustrating exemplary testbuffer multiplexer circuits.

FIG. 3 is a schematic diagram illustrating an exemplary input buffercircuit.

FIG. 4 is a schematic block diagram of an exemplary test input controlbuffer circuit.

FIG. 5 is a schematic block diagram illustrating an exemplary leveldetect circuit.

FIG. 6 is a schematic block diagram illustrating an exemplary circuitfor generating enable test and enable normal signals.

FIG. 7 is a schematic block diagram illustrating an exemplary controlsignal multiplexer circuits.

FIG. 8 is a schematic timing diagram illustrating a set and loadsequence.

FIGS. 9 and 10 are schematic block diagrams illustrating exemplarysoft-blow fuse systems for simulating different fuse configurations inIC devices.

FIG. 11 is a schematic block diagram illustrating an exemplary soft-blowcircuit.

FIG. 12 is a schematic block diagram illustrating an exemplary fusecircuit that can be used in conjunction with a soft-blow circuit.

FIG. 13 is a schematic block diagram illustrating an exemplary voltageregulator that can be tuned by a fuse circuit.

FIGS. 14-16 are flowcharts illustrating methods for testing differentfuse configurations in IC devices.

Like numerals are used for like and corresponding parts in the variousdrawings.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate exemplary semiconductor devices 10 and 50 inwhich systems and methods according to various implementations of theinvention can be implemented and used. The semiconductor devices 10 and50 include a fuse circuit 91 and a corresponding soft-blow (“SB”)circuit 90. The fuse circuit 91 includes one or more fuses that can bepermanently blown, for example, by laser. The semiconductor devices 10and 50 have a test mode in which the soft-blow circuit 90 and fusecircuit 91 can be configured to simulate electric and other operationalconditions which are present when selected fuses are blown in the fusecircuit 91. Thus different fuse configurations can be tested and anoptimal fuse configuration can be identified in the semiconductordevices 10 and 50 without permanently blowing any of the fuses in thefuse circuit 91. Once the optimal fuse configuration has been found, thefuses can be permanently blown, for example, by a laser beam.

Semiconductor devices 10 and 50 are packaged devices each of which caninclude one or more integrated circuit (IC) devices of any type. Withinthe packages, the IC devices may require testing, such as tests forfinding optimal fuse configurations. The tests can be performed, forexample, by external automated test equipment or an integrated circuittester. Each of semiconductor devices 10 and 50 can be packaged as astandard ball grid array (BGA) or thin quad flatpack (TQFP) having 144pins or more. However, other types of packaging may also be used. Forexample, the packaging may have a ceramic base with wire bonding oremploying thin film substrates, and mounting on a silicon substrate or aprinted circuit board (PCB) substrate. The packaging may further utilizevarious surface mount technologies such as a single in-line package(SIP), dual in-line package (DIP), zig-zag in-line package (ZIP),plastic leaded chip carrier (PLCC), small outline package (SOP), thinSOP (TSOP), flatpack, and quad flatpack (QFP), to name but a few, andutilizing various leads (e.g., J-lead, gull-wing lead) or BGA typeconnectors.

FIG. 1A is a block diagram of the exemplary semiconductor device 10. Asdepicted, semiconductor device 10 may comprise a system integratedcircuit (IC) 12 and a memory 14. Each of system IC 12 and memory 14 canbe implemented in a separate semiconductor die (commonly referred to asa “chip”), which is a monolithic structure formed from, for example,silicon or other suitable material. Accordingly, semiconductor device 10can be referred to as a “multi-chip module” (MCM).

System IC 12 can be a chip with logic circuitry, such as, for example,an application specific integrated circuit (ASIC), a processor, amicroprocessor, a microcontroller, a field programmable gate array(FPGA), programmable logic device (PLD), complex programmable logicdevice (CPLD), or other logic device. Memory 14 can be an IC memorychip, such as, for example, static random access memory (SRAM), dynamicrandom access memory (DRAM), synchronous DRAM (SDRAM), non-volatilerandom access memory (NVRAM), and read only memory (ROM), such aserasable programmable ROM (EPROM), electrically erasable programmableROM (EEPROM), and flash memory.

System IC 12 and memory 14 may work in conjunction. Memory 14 providesstorage capability for data/information that is provided from system IC12 or some other components. System IC 12 provides processing capabilityfor operating on data/information, and may retrieve information from andstore information into memory 14. In a normal operation of thesemiconductor device 10, signals for data/information may be received bymemory 14 from system IC 12.

System IC 12 and memory 14 may each comprise one or more bonding pads16, which can be connected via, for example, bonding wires 18, toprovide communication between the chips and/or other components withinor external to semiconductor device 10. As used herein, the terms“connected,” “coupled,” or any variant thereof, means any connection orcoupling, either direct or indirect, between two or more elements. Forclarity, in FIG. 1A, only a portion of the bonding pads 16 and bondingwires 18 are provided with reference numerals. At least some of thebonding pads 16 and bonding wires 18 may support communication directlybetween system IC 12 and memory 14.

In one implementation, memory 14 includes fuse circuit 91 andcorresponding soft-blow circuit 90. Alternatively or in addition, systemIC 14 can also include a fuse circuit and a corresponding soft-blowcircuit. In other implementations, the fuse circuit 91 and thecorresponding soft-blow circuit 90 can be implemented in thesemiconductor device 10 or 50 separately from system IC 12 and memory14.

In one embodiment, system IC 12 and memory 14 may be mounted in aside-by-side arrangement on a printed circuit board (PCB) substrate,such as for a multi-chip package (MCP). Such PCB substrate may also havebonding pads 16 and traces 19. In one embodiment, at least some traces19 formed on either memory 14 or system IC 12 may be used for pin-outfor the other chip.

As shown, semiconductor device 10 includes a number of externalterminals 20 which can be, for example, input/output (I/O) leads orpins. For clarity, in FIG. 1A, only some of the external terminals 20are provided with reference numerals. In general, these externalterminals 20 enable the components within semiconductor device 10 toexchange data/information with components external to device 10. In oneembodiment, one or more of these external terminals 16 may be connectedto and serve both the system IC 12 and memory 14. That is, a terminal 20which provides I/O capability for the system IC 12 may also provide I/Ocapability for memory 14.

To verify that semiconductor device 10 is operating properly, thecomponents contained therein should be thoroughly tested. For example,semiconductor device 10 can be tested for identifying optimalconfiguration for the fuses in fuse circuit 91. For the fuse test,soft-blow circuit 90 and fuse circuit 91 can be programmed to simulatedifferent configurations of blown fuses, without permanently blowing anyof the fuses. Other components of semiconductor device 10 can also betested.

In one embodiment, memory 14 may receive signals from test equipment(not shown) that is external to device 10. One or more test buffermultiplexer circuits 22 may be provided or incorporated in memory 14.Each multiplexer circuit 22 generally functions to multiplex betweensignals that are generated in normal operation of semiconductor device10 and signals that are generated for testing of semiconductor device10. The signals generated in normal operation may originate from systemIC 12, whereas the signals for testing may originate from external testequipment.

Memory 14 may also comprise an on-chip sequence pattern generator, suchas that described in related U.S. patent application Ser. No. 10/205,883entitled “Internally Generating Patterns For Testing In An IntegratedCircuit Device,” filed on Jul. 25, 2002, assigned to the same assigneeand incorporated by reference herein in its entirety. Such patterngenerator may comprise a test column address counter and a test rowaddress counter. The test column address counter may incrementindependently of the test row address counter. The address counters mayfunction to internally generate sequences of numbers for use asaddresses during testing.

If memory 14 were packaged as a discrete component (i.e., separate fromsystem IC 12), thorough testing of the memory would require full accessto all data, control, and access points of memory 14 so that completetest patterns could be input and extracted from the memory. But sincememory 14 is packaged with system IC 12 in semiconductor device 10 andvarious access points of memory 14 are connected to system IC 12 fornormal operation, test buffer multiplexer circuits 22 enable full accessto memory 14 by multiplexing between signals from system IC 12 in normaloperation and signals from external test equipment during testing. Inthis way, the external terminals 20 which are shared between the memory14 and system IC 12 can imitate test pins which would be dedicated ifmemory 14 were packaged separately.

In one embodiment, the signals which are multiplexed can be clock enable(CKE), chip select (CS), row address strobe (RAS), column address strobe(CAS), write enable (WE), data read/write mask (DQM), bank select (BA),all row precharge (AP), bi-directional test data I/O (TD), set (SET),and load (LOAD), and respective testing counterparts for the same. Itshould be understood that, in other embodiments, signals in addition toor other than one or more of those described immediately above may bemultiplexed.

In addition, one or more external terminals 20 may be dedicated (i.e.,not shared between system IC 12 and memory 14) for the testing of memory14. In one embodiment, these dedicated terminals 20 can receive signalsfor test (TEST), analog word-line voltage (VCCP), and analog memorysubstrate voltage (VBB). The TEST signal generally functions to putmemory 14 in a test mode. The VCCP and VBB signals are used forstressing the memory 14 by providing voltage levels significantly aboveor below VDD and VSS. In another embodiment, only one external terminal20—i.e., the one for the TEST signal—is dedicated for the testing ofmemory 14, and the signals for VCCP and VBB are generated internallywithin memory 14. This reduces pin count for the semiconductor device10. In yet another embodiment, the external terminal which receives theTEST signal may be shared between the memory 14 and system IC 12. Insuch case, a voltage level which differs from the voltage levels used innormal operation is applied to the external terminal to put the memory14 into test mode, as discussed herein in more detail.

Semiconductor device 10 can work in normal operation or be placed intest mode. In normal operation, system IC 12 and memory 14 may cooperateto receive, process, store, and output data and information. In testmode, one or both of system IC 12 and memory 14 may be functionallytested to verify proper operation. With embodiments of the presentinvention, memory 14 can be tested completely separately from system IC12.

In one embodiment, semiconductor device 10 (and in particular, memory14) can be placed in test mode with various control signals, such as,for example, the TEST, SET and LOAD signals. Memory 14 may include atest input control buffer circuit 40, which generally functions toreceive and buffer control signals for programming the memory 14. Insome embodiments, the TEST signal is made a high value (or “1”, such asVDD) and remains high throughout in-package testing. The SET and LOADsignals are initially at a low value (or “0”, such as GND). Then the SETand LOAD signals are pulsed high for predetermined periods (e.g., 10 ns)to enable test buffer multiplexer circuits 22 on memory 14. The device10 is now in test mode.

In test mode, there may be two phases: a programming phase and an accessphase. In the programming phase, the memory 14 can be set up orprogrammed for testing. This set up can include, for example, loadingtest addresses and sequential test data patterns (or codes) into variousparts of the memory 14 (e.g., row and column test counters). The set upcan also include programming of the soft-blow circuit 90. In oneembodiment, one or more test data (TDQ) signals may be used to programtest modes, load test addresses, load test vectors, and load testpatterns. The SET and LOAD signals can be used to enable test addressesor vectors to be set and loaded. An exemplary timing diagramillustrating the pulses for SET and LOAD signals to program a code inmemory 14 is shown and described with reference to FIG. 8 below. Alltest mode programming can be performed asynchronously (i.e., no clock isrequired). In one embodiment, a test control (TCNT) is set to a highvalue (“1”) to cause the memory 14 to exit the programming phase andenter the access phase. New test addresses and vectors can no longer beprogrammed.

In the access phase, the memory 14 is actually operated using the testaddresses and test patterns. In one embodiment, all external and burstcounter addresses are ignored by memory 14 while in access phase. Thememory 14 only recognizes the addresses from the programmed row andcolumn test counters. The TDQ signals are now used to read and writedata to memory 14. A test stop row (TSR) counter signal may be used tostop the row address counter, and a test stop column (TSC) countersignal may be used to stop the column address counter while in accessphase. This allows independent incrementation (or decrementation) of rowand column addresses. Both the TSR and TSC counter signals may beindependent of the CLK signal. In general, with some embodiments,programming of memory 14 during testing can be asynchronous. In otherembodiments or as an option, programming can be synchronous for memory14. Also, during access phase, the memory 14 may operate synchronouslyor asynchronously, depending on the memory specification.

To exit test mode, in one embodiment, the TEST signal is brought to alow value (“0”), which clears all test operations and disables the testinput buffers.

With the systems and methods, according to various embodiments of theinvention, an IC chip (e.g., memory 14) which is packaged along with oneor more other chips (e.g., system IC 12) can be fully tested withoutrequiring a significant number of dedicated I/O terminals. Controlsignals from complex external test equipment (e.g., a standard externalmemory tester) can be provided to all data, control, and access pads ofthe desired IC chip for thorough and complete testing using a variety oftest patterns and sequences. Furthermore, the IC chip can include fusesand corresponding soft-blow circuits to fine tune electric or otheroperational characteristics. These embodiments provide complete andflexible testing of IC devices.

In some embodiments, the systems and methods described herein can beused in conjunction with the systems and methods described in relatedU.S. patent application Ser. No. 09/666,208 entitled “Chip TestingWithin a Multi-Chip Semiconductor Package,” filed on Sep. 21, 2000,assigned to the same assignee and incorporated by reference herein inits entirety.

FIG. 1B is a block diagram of another exemplary semiconductor device 50,according to an embodiment of the present invention. Semiconductordevice 50 can be similar in many respects to semiconductor device 10depicted in FIG. 1A. That is, semiconductor device 50 may comprise asystem IC 12 and a memory 14 (each with bonding pads 16 providedthereon), and external terminals 20 for communicating data/informationinto and out of semiconductor device 50. Memory 14 receives signals fromsystem IC 12. Furthermore, memory 14 may comprise one or more testbuffer multiplexer circuits 22 for enabling multiplexing between signalsgenerated in normal operation and signals generated for testing, therebyallowing memory 14 to be thoroughly tested with external test equipment.Memory 14 can also include fuse circuit 91 and corresponding soft-blowcircuit 90. Alternatively or in addition, system IC 14 or another ICdevice within the semiconductor device 50 can also include one or morefuse circuits and corresponding soft-blow circuits.

In semiconductor device 50, system IC 12 and a memory 14 are provided instacked arrangement. In this arrangement, system IC 12 may be attachedto memory 14 using, for example, any suitable adhesive. Traces 19 may beformed on memory 14 for pin-out for system IC 12. Furthermore, althoughnot depicted, some traces 19 may be formed on system IC 12 for pin-outfor memory 14.

In one embodiment, one or both of the test analog voltages (i.e.,word-line voltage (VCCP) and analog memory substrate voltage (VBB)) canbe multiplexed with voltages used in normal operation. For this,respective test buffer multiplexer circuits 22 may be provided orincorporated in memory 14.

Test Buffer Multiplexer Circuit

FIG. 2A is schematic diagram of an exemplary implementation of the testbuffer multiplexer circuit 22 (FIGS. 1A and 1B). Test buffer multiplexercircuit 22 may be implemented or incorporated in the memory 14 tosupport its testing. In this embodiment, as depicted, test buffermultiplexer circuit 22 comprises buffer circuits 30 a, 30 b and passgate circuits 32 a, 32 b.

One buffer circuit 30 b may be connected to receive a signal (e.g., data(DQ)) from system IC 12, while the other buffer circuit 30 a may beconnected to receive a corresponding test signal (e.g., test data (TDQ))from a testing machine via an external terminal 20. Buffer circuit 30 ais enabled by an enable test (ET) signal, while buffer circuit 30 b isenabled with an enable normal (EN) signal. The ET and the EN signals canbe complementary signals, and may both be supported by the same externalpin or lead which, for example, receives the TEST signal. This externalpin can be either dedicated for receiving the TEST signal to the placethe memory 14 in test mode, or alternatively, shared between the memory14 and a system IC 12. An exemplary implementation of a buffer circuit30 is depicted in FIG. 3.

Pass gate circuit 32 a is coupled at its input to receive the output ofbuffer circuit 30 a. Pass gate circuit 32 b is coupled at its input toreceive the output of buffer circuit 30 b. Both pass gate circuits 32receive the enable test and enable normal signals. Each pass gatecircuits 32 generally function to pass the value of a signal appearingat its input as the value of its output signal upon a particularcombination of values for the enable test and enable normal signals. Forexample, in one embodiment, when the enable test signal has a high value(or “1”) and the enable normal has a low value (or “0”), then the valueof the output signal from buffer circuit 30 a appears at output Y forthe test buffer multiplexer circuit 22. An exemplary implementation ofpass gate circuit 32 is described in related U.S. application Ser. No.09/967,389 entitled “Testing of Integrated Circuit Devices,” filed onSep. 28, 2001, assigned to the same assignee and incorporated byreference herein in its entirety.

Although only a single test buffer circuit 22 is depicted here in FIG.2A for the data signal and its counterpart test signal, it should beunderstood that a plurality of test buffer circuits 22 may be providedon a memory 14 for multiplexing various other signals from a system IC12 (e.g., CLK, CKE, CS, RAS, CAS, WE, DQM, BA, and AP) and theircounterpart test signals (e.g., TCLK, TCKE, TCS, TRAS, TCAS, TWE, TDQM,TBA, and TAP).

In operation, when the memory 14 on which test buffer multiplexercircuit 22 is implemented is in normal operation, then the value of thesignal from the system IC (e.g., DQ) is buffered and passed as theoutput Y of the multiplexer circuit 22. Alternatively, when the memory14 is placed in test mode, then the value of signal from externaltesting equipment (e.g., TDQ) is buffered and passed as the output Y ofthe multiplexer circuit 22.

FIG. 2B is schematic diagram of another exemplary implementation of thetest buffer multiplexer circuit 22 (FIGS. 1A and 1B). In thisembodiment, as depicted, test buffer multiplexer circuit 22 comprisesbuffer circuits 34 a, 34 b and NAND gate 36.

Buffer circuits 34 b may be connected to receive a signal (e.g., data(DQ)) from system IC 12, and buffer circuit 34 a may be connected toreceive a corresponding test signal (e.g., test data (TDQ)) from atesting machine via an external terminal 20. Buffer circuits 34 a and 34b are enabled by the enable test (ET) and enable normal (EN) signals,respectively. NAND gate 36 receives and performs a “NAND” operation onthe outputs of buffer circuits 34 a and 34 b. NAND gate 36 outputs avalue of the Y signal, which is the output for the multiplexer circuit22.

As with FIG. 2A, although only a single test buffer circuit 22 isdepicted here in FIG. 2B for the data signal and its counterpart testsignal, it should be understood that a plurality of test buffer circuits22 may be provided on the memory 14 for multiplexing various othersignals from a system IC 12 and their counterpart test signals.

FIG. 2C is schematic diagram of yet another exemplary implementation ofthe test buffer multiplexer circuit 22 (FIGS. 1A and 1B). In thisembodiment, as depicted, test buffer multiplexer circuit 22 comprisesbuffer circuits 50 a, 50 b, 50 c, inverter gates 52 a, 52 b, 52 c, 52 d,data buffers 54 a, 54 b, a multiplexer (MUX) 56, and a NOR gate 58.

Buffer circuit 50 a and inverter gates 52 a, 52 b may be part of a pathfor inputting program code data into memory 14, for example, during aprogramming phase of test mode for the memory 14. Buffer circuit 50 amay receive a test signal (e.g., test data (TDQ)) from an external testmachine. Buffer circuit 50 a can be enabled by a signal that is derivedfrom logic operations on the enable test (ET) and a test control or testcounter (TCNT) signal. The output of this buffer circuit 50 a andinverter gates 52 a, 52 b is a TDA signal for programming memory 14. Inone embodiment, eight TDA signals (i.e., TDA[0:7]) may be supported forprogramming up to 256 test codes. Eight TDQ signals (i.e., TDQ[0:7]) maybe supported as well.

In one embodiment, the TCNT signal may default to a low value upon entryinto test mode. If the memory 14 is in the programming phase of testmode, the TCNT signal may have a low value. If memory 14 is in theaccess phase of test mode, test control (TCNT) signal may have a highvalue. TCNT signal may be set to a high value using the SET and LOAD(code) signals. For example, in one embodiment, the TCNT signal can beset to VDD by bringing the SET signal to a high value with the values ofTDQ[7:0]=00110000. The LOAD signal is used for loading registers withtest data, such as test address or test pattern or fuse configuration.

Buffer circuit 50 b and data buffer 54 a may be part of a path forinputting test data into memory 14, for example, during an access phaseof test mode for the memory 14. Buffer circuit 50 b is enabled by theenable test (ET) signal and may receive the test data (TDQ)) from anexternal test machine. Data buffer 54 a is connected to receive theoutput signal of buffer circuit 50 b and a clock (CLK) signal. Databuffer 54 a latches the output of circuit 50 b and may output the sameon an edge of the CLK signal.

Buffer circuit 50 c and data buffer 54 b may be part of a path forinputting data into memory 14, for example, during normal operation forthe memory 14. Buffer circuit 50 c is enabled by the enable normal (EN)signal and may receive the data (DQ)) from system IC 12. Data buffer 54b is connected to receive the output signal of buffer circuit 50 c and aclock (CLK) signal. Data buffer 54 b latches the output of circuit 50 cand may output the same on an edge of the CLK signal.

Multiplexer 56 is connected to receive the output signals of databuffers 54 a and 54 b, and can be enabled with a TEST signal, a TSTENsignal, or a TCNT signal. Depending on the values of the EN and ETsignals, multiplexer 56 will pass (via inverter gate 52 c) either theoutput of data buffer 54 a or the output of data buffer 54 b to othercircuitry on memory 14. In particular, if memory 14 is in test mode(access phase), the output of data buffer 54 a is provided to the memory14 for testing of same. If memory 14 is in normal operating mode, theoutput of data buffer 54 a is provided to the memory 14. In otherembodiments, other circuit, such as a NAND gate, can be used instead ofmultiplexer 56.

Test Input Control Buffer Circuits

FIG. 4 is a schematic diagram of an exemplary implementation of the testinput control buffer circuit 40 (FIGS. 1A and 1B). Test input controlbuffer circuit 40 may be implemented or incorporated in the memory 14 tosupporting the testing thereof. Test input control buffer circuit 40generally functions to receive and buffer control signals forprogramming of memory 14 during the programming phase of test mode. Asdepicted, test control buffer circuit 40 comprises a level detectcircuit 42, input buffer circuits 44 a, 44 b, and 44 c, and invertergates 46 a, 46 b, and 46 c.

Level detect circuit 42 is optional and can be provided as part of testinput control buffer circuit 40 when the external pin or lead forreceiving the TEST signal is shared between the memory 14 and a systemIC 12. In such case, because it would be undesirable to inadvertentlyplace memory 14 into test mode during normal operation, a voltage levelwhich differs from the voltage levels used in normal operation is usedfor putting the memory 14 into test mode. This voltage level can be, forexample, a negative voltage (e.g., −3V) or a higher than normal voltage(e.g., 7V if VDD for memory 14 is 3.3V). Level detect circuit 42receives the external TEST signal (XTEST) and generates an internal testenable (TSTEN) signal that is provided to each of input buffer circuits44 a, 44 b, and 44 c. The TSTEN signal enables input buffer circuits 44.An exemplary implementation for level detect circuit 42 is depicted inFIG. 5.

Referring again to FIG. 4, if the external pin for receiving the TESTsignal is dedicated, level detect circuit 42 is not needed and thuswould not be present in test input control buffer circuit 40. In thiscase, the external TEST signal can be applied directly to input buffercircuits 44. In one embodiment, for this situation, a high value for theTEST signal causes memory 14 to be in test mode, while a low value forthe TEST signal takes memory 14 out of test mode.

A separate combination of input buffer circuit 44 and inverter gate 46is provided for each of a number of programming control (PRG) signals,such as, for example, the SET, LOAD, and RESET signals. For eachcombination, when the input buffer circuit 44 is enabled, the respectivecontrol signal is buffered in circuit 44 and output to the inverter gate46 where the signal is inverted. The output of each inverter gate 46 isa respective program P signal (separately labeled P1, P2, P3). Theprogram P signals may be provided to control the test programming of thememory 14 when it is in the programming phase of test mode. For example,these program P signals can be used to set flags and other conditions inmemory 14.

It should be noted that in alternative implementations for a test inputcontrol buffer circuit 40, any number of input buffer circuits 44 andinverter gates 46, or any other suitable element could be used tosupport control signals that are in addition to, or instead of, thespecific signals depicted in FIG. 4.

Enable Test and Enable Normal

FIG. 6 is a schematic diagram of an exemplary implementation of acircuit 80 for generating the enable test (ET) and the enable normal(EN) signals. As depicted, this circuit 80 comprises NAND gates 82 a, 82b, 82 c, delay circuits 84 a, 84 b, and inverter gates 86 a, 86 b, and86 c.

NAND gate 82 a can be connected to receive the program P and TSTENsignals from the test input control buffer circuit 40 (FIGS. 1A, 1B and4). The program P signals can be associated with or correspond to theSET, LOAD, and RESET signals. The delay circuits 84 a and 84 b delay theoutput generated by the NAND gate 82 a. The delay circuits 84 a and 84 bmay also filter noise or voltage spikes, and may prevent unintentionalentry into test mode. Delay circuits 84 a and 84 b may be replaced witha single, larger delay circuit in alternative embodiments.

NAND gates 82 b and 82 c are cross-connected at one input each. Theother input of NAND gate 82 b is connected to receive the output ofdelay circuit 84 b. The other input of NAND gate 82 b is connected toreceive a test reset (TR) signal. The test reset signal, which may bederived from a reset signal, can be used to reset an individual testmode without completely exiting test mode. Inverter gates 86 a and 86 bare connected to receive the output of NAND gate 82 b, while NAND gate82 d and inverter gate 86 c are connected to receive the output of NANDgate 82 c. The output of inverter gate 86 b is the enable test (ET)signal, and the output of inverter gate 86 c is the enable normal (EN)signal. The ET and EN signals may be applied to the test buffermultiplexer circuit 22 (see FIGS. 1A, 1B, 2A, 2B, and 2C).

In operation, depending on the combination of values for the TSTEN andprogram P signals, circuit 80 will output particular values for theenable test (ET) and the enable normal (EN) signals for enabling thetest or normal buffers.

Control Signal Multiplexer Circuits

FIG. 7 is a schematic diagram of an exemplary implementation of controlsignal multiplexer circuits 60 a, 60 b, and 60 c. Control signalmultiplexer circuits 60 may be implemented or incorporated in the memory14 (FIGS. 1A and 1B) to support its testing.

In general, each control signal multiplexer circuit 60 functions toreceive, multiplex, and buffer a control signal and its counterpart testsignal. These control signals can be, for example, an active (ACT)signal, a read (RD) signal, and a write (WR) signal, and the counterparttest signals can be a test ACT (TACT) signal, a test RD (TRD) signal,and a test WR (TWR) signal, respectively. The control signals (ACT, RD,and WR) may be received at pads 16 on memory 14 which are coupled to thesystem IC 12. The respective counterpart test signals (TACT, TRD, andTWR) may be received at pads which are connected to external terminals20 that are shared between memory 14 and system IC 12. It should beunderstood, that in other embodiments, control signals in addition to orother than one or more of those described immediately above may bemultiplexed.

As depicted, each control signal multiplexer circuit 60 comprises amultiplex buffer 62 (separately labeled 62 a, 62 b, and 62 d) coupled toa plurality of inverter gates 64 (separately labeled 64 a-64 i).

In one embodiment, each multiplexer buffer 62 can be implemented withsubstantially similar circuitry as used for either of theimplementations of test buffer multiplexer circuit 22 depicted in FIGS.2A and 2B. Each multiplex buffer 62 receives an enable test (ET) signal,an enable normal (EN) signal, a respective control signal, and thecounterpart test signal. During normal operation for memory 14,multiplex buffer 62 is enabled by the enable normal signal, which allowsthe respective control signal (e.g., ACT, RD, or WR) to be buffered andoutput by the multiplex buffer 62. In test mode, multiplex buffer 62 isenabled by the enable test signal, which allows the respectivecounterpart test signal (e.g., TACT, TRD, or TWR) to be buffered andoutput by the multiplex buffer 62.

The output signal from a multiplex buffer 62 is provided to the first ina respective sequence of inverter gates 64. As shown, three inventorgates 64 are provided in each sequence. The output of the last invertergate 64 of each sequence is provided as a control signal to memory 14,for either normal operation or testing (depending on the ET and ENsignals).

It should be noted that other control signal multiplexer circuits 60 maybe provided to support control signals that are in addition to, orinstead of, the specific signals depicted in FIG. 7.

Set and Load Sequence

FIG. 8 is an exemplary timing diagram of a set and load sequence 70.When memory 14 (FIGS. 1A and 1B) is in test mode, sequence 70 can beused to load codes into memory 14 during the programming phase. Inparticular, in one embodiment, test modes, test patterns and testaddresses may be programmed in this phase. The set and load sequence 70can also be used to program different fuse configurations.

Referring to FIG. 8, waveforms 72, 74, and 76 are given for the SETsignal, the LOAD signal, and a TDQ signal. One or more TDQ signals maybe used to read and write test data, set test mode codes, load row andcolumn addresses, program least significant bits (LSB) for row andcolumn counters, and load test data patterns. In one embodiment, therecan be eight TDQ signals: TDQ[0:7]. As the exemplary waveforms in FIG. 8illustrate, the programming for testing memory 14 can be performedasynchronously (i.e., without a clock signal). The SET and LOAD signalsare used to input codes for setting test modes and enable test addressor vectors to be loaded. These codes may be provided in the one or moreTDQ signals. The codes can indicate or represent, for example, any ofthe following: no test, load row address mode, reserve, load columnaddress mode, set row counter LSB, set/load test data backgroundequations, all even row enable, all odd row enable, disable all pumpsand regulators, disable redundant rows and columns, set column counterLSB, start test counter, load data pattern, set row counter count down,set column counter count down, and individual DQ access mode.

For example, in one embodiment, to load an initial burst column address(i.e., the starting address in a column burst counter), the followingcommand is issued using the timing shown in FIG. 8:

-   -   SET=1 with TDQ[7:0]=00000011 this sets the “Load Column Address”        bit active (e.g., LCA=1).    -   LOAD=1 with TDQ[7:0]=“start address” load value at TDQs to the        column address counter.

For setting just a test mode (e.g., disabling a voltage regulator,setting access phase (i.e., TCNT=1), or setting 8×parallel test modes),then the SET signal in combination with valid TDQs is sufficient. In oneembodiment, test modes can be persistent or non-persistent. Test modesthat are non-persistent go away once a new code is programmed. Testmodes that are persistent will remain in effect even after a new code isprogrammed.

Fuse Configurations

FIG. 9 schematically illustrates an exemplary soft-blow fuse systemincluding the fuse circuit 91 and the corresponding soft-blow circuit90. The fuse circuit 91 includes one or more fuses 92 that can bepermanently blown, for example, by laser. During testing, however, thesoft-blow circuit 90 and the fuse circuit 91 can be programmed withoutpermanently blowing the fuses 92 to generate electric and otheroperational conditions that are present if some of the fuses 92 wereactually blown. For example, the soft-blow circuit 90 and fuse circuit91 can be implemented in semiconductor devices 10 and 50 (FIGS. 1A and1B) to simulate electric and other operational conditions which arepresent when fuses 92 are selectively blown in the fuse circuit 91. Thusdifferent fuse configurations can be tested and an optimal fuseconfiguration can be identified without permanently blowing any of thefuses 92 in the fuse circuit 91 during the test. Once the optimal fuseconfiguration has been found, the fuses 92 can be permanently blown, forexample, by a laser beam.

In the implementation shown in FIG. 9, the soft-blow circuit 90 receivesone or more data signals 93, an enable signal 94 and a test signal 95.The data signals 93 define a simulated fuse configuration, and theenable and test signals 94 and 95 can be used to control operationsrelated to the testing of the different fuse configurations. In otherimplementations, the soft-blow circuit 90 can receive alternative oradditional signals to control the fuse configuration test.

The data signals 93, enable signal 94 and test signal 95 can be receivedon multiple input lines. For example, each of the data signals 93,enable signal 94 and test signal 95 can be received on a separate inputline. Alternatively, multiple signals can be received on a single inputline. For example, multiple data signals 93 can be received sequentiallythrough a single serial input line. Or the enable and test signals 94and 95 can be received through the same or a different serial inputline. In one implementation, the enable signal 94 also contains testinformation. For example, the enable and test signals 94 and 95 can becombined by an AND operation and driven using a single line.

The data signals 93 can define the fuse configuration directly orindirectly. In one implementation, each data signal 93 directlycorresponds to a respective fuse 92, and the level of the data signal 93directly determines whether the respective fuse 92 should be blown ornot in the simulated fuse configuration. Alternatively, the data signals93 can include short codes that correspond to different fuseconfigurations whose details are defined internally within the soft-blowcircuit 90. Using such codes might be advantageous when the fuse circuit91 includes a large number of fuses 92 but operational requirementslimit the possible fuse configurations.

The enable and test signals 94 and 95 control operations related to thetesting of the different fuse configurations. In one implementation, thetest signal 95 activates the soft-blow circuit 90 and the enable signal94 controls inputting the data signals 93 into the soft-blow circuit 90.For example, the test signal 95 can correspond to the TEST signal thatputs the entire semiconductor device 10 into a test mode (FIG. 1A).Thus, the TEST signal activates the soft-blow circuit 90 in the testmode and disables it during normal operation. Furthermore, the enablesignal 94 can be implemented to control data input through the datasignals 93 into the soft-blow circuit 90 during a programming phase inaccordance with the TEST, SET and LOAD signals which control the entiretest of the semiconductor device 10.

The soft-blow circuit 90 generates soft-blow (“SB”) signals 96 that aretransmitted to the fuse circuit 91 to determine the simulatedconfiguration for the fuses 92. For each allowable configuration of thefuses 92, the fuse circuit 91 has a corresponding state of operationthat can be set by the soft-blow signals 96. The same state of operationcan also be set by permanently blowing selected fuses 92. Or the stateof operation can be set by the soft-blow signals 96 in combination withpermanently blown fuses 92.

In one implementation, soft-blow signals 96 have a default value duringnormal operation so that the fuse circuit's state of operation isdetermined only by the configuration of permanently blown fuses 92;during testing, however, the fuse circuit's state of operation isdetermined only by the soft-blow signals 96. Thus, different fuseconfigurations can be simulated during the test without actuallychanging the configuration of permanently blown fuses 92. The soft-blowcircuit 90 can also include initialization circuitry to ensure that thesoft-blow signals 96 take their default value at startup and afterreturning from test to normal mode of operation.

In alternative implementations, the fuse circuit's state of operationcan be determined as a function of both the soft-blow signals 96 and thepermanently blown fuses 92 during the test. Or the soft-blow signals 96can be effective to determine the fuse circuit's state of operation notonly during the test but during the normal mode of operation as well.

FIG. 10 schematically illustrates an exemplary implementation of asoft-blow fuse system that can be implemented in semiconductor devices10 and 50 (FIGS. 1A and 1B). In the exemplary implementation, the systemincludes a latch array circuit 100 and a fuse array circuit 105. Thelatch and fuse array circuits 100 and 105 can be implemented in the sameor different chips. If implemented in the same chip, the latch and fusearray circuits 100 and 105 can be located in a designated area of thechip relatively close to each other. Thus wiring between the latch andfuse circuits 100 and 105 can be minimized. Alternatively, the latch andfuse array circuits 100 and 105 can be implemented in any otherconfiguration which suits the particular design of the semiconductordevice in that chip.

The latch array circuit 100 is controlled by test signal 103 and enablesignal 104 to receive DQ0-DQ7 data signals 102 that define a fuseconfiguration during testing. The latch array circuit 100 generatesSB0-SB7 soft-blow signals in accordance with the test, enable andDQ0-DQ7 data signals 103, 104 and 102, respectively. The SB0-SB7soft-blow signals are transmitted to the fuse array circuit 105 todetermine the fuse configuration in accordance with the data signals102. The fuse array circuit 105 generates Tune0-Tune7 signals 107 thatare determined by the current fuse configuration to fine tune oroptimize other components of the semiconductor device.

In one implementation, the soft-blow fuse system uses Test DQ signals(TDQ<0:7>; not shown) in addition to using the normal DQ0-DQ7 datasignals. The Test DQ signals can be implemented to allow for morelogistical flexibility. For example in a SiP package, the TDQ<0:7>signals can also be used to program the “soft fuses.” Thus each fuse canbe addressed using the TDQ or DQ signals, which allows electricallyprogramming the fuses by adding a “program line” that can be implementedin a non-volatile structure, such as a one-time programmable memory cellor anti-fuse. Such a program line may be brought to a desiredprogramming voltage level to switch the memory bit or blow theanti-fuse. In this case, either an external tester or the secondary IC(e.g. ASIC) can run a soft-fuse test program and then program the fusesaccording to the results of the test.

The latch array circuit 100 includes Latch0-Latch7 latches 101. Each ofthe Latch0-Latch7 latches 101 receives the test and enable signals 103and 104 along with a respective one of the DQ0-DQ7 data signals 102.Thus, Latch0 receives DQ0 data signal, Latch1 receives DQ1 data signal,. . . etc., and Latch7 receives DQ7 data signal. Based on the receivedsignals, each of the Latch0-Latch7 latches 101 generates a respectiveone of the SB0-SB7 soft-blow signals 108. Thus, Latch0 generates SB0soft-blow signal, Latch1 generates SB1 soft-blow signal, . . . etc., andLatch7 generates SB7 soft-blow signal.

Each of the Latch0-Latch7 latches 101 is controlled by the test andenable signals 103 and 104. In one implementation, the test signal 103corresponds to the TEST signal whose active value puts the entiresemiconductor device, including the soft-blow fuse system, into a testmode. Thus in the test mode, the enable signal 104 can control receiving(“latching on”) the DQ0-DQ7 data signals 102 and outputting the SB0-SB7soft-blow signals 108 in accordance with the received DQ0-DQ7 datasignals. The TEST signal's inactive value, on the other hand, can setthe device into the normal operation mode in which the SB0-SB7 soft-blowsignals 108 have a default value that is independent of the enable anddata signals 104 and 102, and sets the fuse array circuit 105 into astate of operation corresponding to the permanently blown fuses.

The fuse array circuit 105 includes Fuse0-Fuse7 single-fuse units 106.Each of the single-fuse units 106 receives a respective one of theSB0-SB7 soft-blow signals and includes a single fuse that can bepermanently blown, for example, by laser. Based on the respectivesoft-blow signal and the fuse's permanent state (blown or intact), eachof the single-fuse units 106 generates a respective one of theTune0-Tune7 signals 107. If the respective soft-blow signal has anon-active (default) value (for example, in the normal operation mode),the single-fuse unit can generate a respective Tune signal value thatdepends only on the fuse's permanent state in that unit. If therespective soft-blow signal has an active (non-default) value (forexample, in the test mode of operation), the single-fuse unit cangenerate a respective Tune signal whose value corresponds to a state ofoperation in which the unit's fuse is permanently blown. Thus, a “blown”value of the Tune signal can be generated during a test even if theunit's fuse is not permanently blown. Such simulated “soft blow” of thefuse allows testing different fuse configurations to fine tune oroptimize the device's operation.

In alternative implementations, the latch array circuit 100 and fusearray circuit 105 can include more, less, or a non-matching number oflatches 101 and single-fuse units 106. Furthermore, the latches 101 andsingle fuse units 106 can be differently organized. For example, onelatch can generate a soft-blow signal value that is transmitted to morethan one of the single-fuse units. Or a single-fuse unit can receive andcombine soft-blow signals from more than one of the latches.

FIG. 11 schematically illustrates an exemplary soft-blow circuit 110.The soft-blow circuit 110 can be used to implement, for example,soft-blow circuit 90 shown in FIG. 9 or any of the Latch0-Latch7 latches101 shown in FIG. 10. The soft-blow circuit 110 receives soft fuseconfiguration data 111 and outputs a soft-blow signal 118 that can beused to control an operational state of a fuse circuit, such as the fusecircuit 91 including the one or more fuses 92 (FIG. 9). The soft-blowcircuit 110 also receives enable and test signals 112 and 113,respectively, that control receiving the fuse configuration data 111 andoutputting the soft-blow signal 118.

In the particular implementation, the soft-blow circuit 110 includesNAND gates 114, 115 and 116, and an inverter 117. The NAND gate 114receives the data signal 111 and the enable signal 112. The NAND gates115 and 116 define an internal state of the soft-blow circuit 110, andthe inverter 117 outputs the soft-blow signal 118. The NAND gate 116also receives the test signal 113 which enables or disables thesoft-blow circuit 110.

The NAND gate 114 receives the enable signal 112 to enable or disablereceiving the data signal 111. If the enable signal 112 is inactive(i.e., has a value corresponding to logical ZERO), the output of theNAND gate 114 is a logical “ONE” independent of the value of the datasignal 111. Thus, receiving the data signal 111 is disabled. If theenable signal 112 is active, the output of the NAND gate 114 correspondsto the inverse of the data signal 111. Thus, receiving the data signal111 is enabled. In alternative implementations, the soft blow circuit110 can receive additional signals to control receiving the data signal111.

The NAND gate 116 receives the test signal 113 to enable or disable theoutput of the soft-blow circuit 110. If the test signal 113 is inactive(i.e., has a value corresponding to logical ZERO), the output of theNAND gate 116 becomes a logical “ONE” and the soft-blow signal 118becomes inactive (default value of logical ZERO) independent of theinternal state of the soft-blow circuit 110. Thus, the output of thesoft-blow circuit 110 is disabled. If the test signal 113 is active, theoutput of the NAND gate 116 can follow the internal state of thesoft-blow circuit 110. Thus, the soft-blow signal 118 can take anon-default value and the output of the soft-blow circuit 110 isenabled. In alternative implementations, the soft blow circuit 110 canreceive additional signals to control its output.

The NAND gates 115 and 116 define an internal state that can be set inaccordance with the enabled data signal 111. The internal state becomesa default state each time when both of the test and enable signals 113and 112 are inactive (ZERO). The default state corresponds to thedefault (intact fuse) value of the soft-blow signal 118. The defaultstate is maintained as the test signal 113 becomes active (ONE) whilethe enable signal 112 remains inactive (ZERO). When the enable signal112 also becomes active (ONE), the internal state can be changed fromdefault to “blown” in accordance with the fuse configuration data signal111. Once the internal state becomes “blown,” the soft-blow signal 118remains active (ONE) even if the enable signal 112 becomes inactiveagain (while the test signal 113 remains active). The internal state andthe soft-blow signal 118 become default again when the test signal 113also becomes inactive (ZERO). Thus, the soft-blow circuit 110 can be setto generate an active soft-blow signal 118 and maintain that activevalue while the test signal 113 is active. In alternativeimplementations, the soft-blow circuit 110 can include additional logicsor receive additional signals, such as a direct “reset” signal.

FIG. 12 schematically illustrates a fuse circuit 120. The fuse circuit120 can be used to implement, for example, fuse circuit 91 shown in FIG.9 or any of the Fuse0-Fuse7 single-fuse units shown in FIG. 10. The fusecircuit 120 receives a soft-blow signal 128 that can be generated by asoft-blow circuit, such as those shown in FIGS. 9-11. The fuse circuit120 includes a fuse 121 which can be blown, for example, by a laserbeam. The fuse circuit 120 generates a tune signal 127 based on thesoft-blow signal 128 and the intact or blown state of the fuse 121. Thetune signal 127 can be used to fine tune other circuit elements, such asvoltage regulators and delay elements in the semiconductor device.

In the particular implementation, the fuse circuit 120 also includes aninverter 122, a resistor 123, and a NOR gate 126. The inverter 122 andthe resistor 123 generate a hard-blow signal 124 in accordance with theintact or blown state of the fuse 121. If the fuse 121 is intact, theinverter 122 receives a high voltage level and outputs a non-active(ZERO) hard-blow signal 124. If the fuse 121 is blown, the resistor 123pulls the input of the inverter 122 to a low voltage level, thus theinverter 122 outputs an active (ONE) hard-blow signal 124.

The NOR gate 126 combines the hard-blow signal 124 with the soft-blowsignal 128 to generate the tune signal 127. The tune signal 127represents a logical ONE only if both of the soft-blow and hard-blowsignals 128 and 124 has a logical ZERO value (corresponding to intactfuse). If either of the soft-blow and hard-blow signals 128 and 124 hasa logical ONE value (corresponding to “blown” fuse), the tune signal 127represents logical ZERO. Thus, the tune signal 127 can be set to ZEROnot only by permanently blowing the fuse 121, but also by providing anactive soft-blow signal 128. Accordingly, the effect of the permanentlyblown fuse 121 can be simulated without actually blowing the fuse 121.

In alternative implementations, the fuse circuit 120 can includeadditional or different circuit elements. For example, the fuse circuit120 can include circuitry to ensure proper initialization upon power-onor reset. Or the fuse circuit 120 can perform a different logicalcombination of the hard-blow and soft-blow signals 128 and 124. The fusecircuit 120 can also receive additional or different control signals,such as reset or normal operation enable signals.

FIG. 13 schematically illustrates an exemplary voltage regulator 130.The voltage regulator 130 receives a tune signal 137 and outputs aregulated voltage signal 139 in accordance with the received tune signal137. The tune signal 137 can be generated by a fuse circuit, such asthat shown in FIGS. 9, 10 and 12, in which one or more fuses define afuse configuration that can be set with or without permanently blowingthe fuses in the fuse circuit. Thus, the voltage regulator 130 can betested without permanently blowing the fuse which tunes the voltageregulator 130 during normal operation.

In the particular implementation, the voltage regulator 130 includes aresistor chain 131-133, a multiplexer 134 and an amplifier 135. Theresistor chain 131-133 generates multiple different voltage levels thatare received by the multiplexer 134. The multiplexer 134 also receivesthe tune signal 137 to select one of the multiple different voltagelevels as its output. The output of multiplexer 134 is received by theamplifier 135 which generates the regulated voltage signal 139 as thevoltage regulator's output.

In alternative implementations, the voltage regulator 130 can includeadditional or different circuit elements. For example, the voltageregulator 130 can include circuitry to ensure proper initialization uponpower-on or reset. The voltage regulator 130 can also receive additionalor different control signals, such as reset signals.

FIG. 14 illustrates a method 140 for testing an IC device that includesa soft-blow fuse system with one or more soft-blow fuses, such as thoseillustrated in FIGS. 9-12. The method 140 can be implemented by a testsystem that is configured to test IC devices with soft-blow fuses.

The test system puts the IC device into a test mode (step 141). Forexample, the system can activate a TEST signal that puts the entire ICdevice into a test mode. Or, the test system can activate only thesoft-blow fuse system of the IC device.

The test system tests the same IC device for multiple different fuseconfigurations (step 143). The different fuse configurations can beimplemented in the IC device without permanently blowing any of thefuses. For example, the different fuse configurations can be programmedinto a soft-blow circuit of the IC device during the test. In oneimplementation, the test is performed for multiple different fuseconfigurations without removing the IC device from the test system.

The test system completes the test by exiting from the test mode andputting the IC device into its normal mode of operation (step 145).Based on the test results for the different fuse configurations, thetest system determines an optimal fuse configuration and permanentlyblows fuses in the IC device according to the optimal fuse configuration(step 147).

FIG. 15 illustrates a method 150 for determining an optimal fuseconfiguration by testing an IC device that includes a soft-blow fusesystem with one or more soft-blow fuses, such as those illustrated inFIGS. 9-12. The method 150 can be implemented by a test system that isconfigured to test IC devices with soft-blow fuses. For example, themethod 150 can be implemented to determine the optimal fuseconfiguration used in the method 140 (FIG. 14).

The test system programs a fuse configuration into the soft-fuse systemof the IC device during the test (step 152). For example, the fuseconfiguration can be programmed by loading fuse configuration data intosoft-blow circuits of the soft-blow fuse system. Or the test system canactivate a fuse configuration which has been pre-programmed in thesoft-blow circuits.

The test system measures operational parameters in the currentlyprogrammed fuse configuration (step 154). The measured operationalparameters can include voltage levels, error rates, delays, or any otherperformance measure of the IC device.

The test system determines whether a new fuse configuration should betested (decision 156). If a new configuration is required (“Yes” branchof decision 156), the test systems programs the new configuration intothe soft-fuse system (step 152). The new fuse configuration can betested without removing the IC device from the test system. If no morefuse configurations should be tested (“No” branch of decision 156), thetest system determines an optimal fuse configuration based on themeasured operational parameters (step 158).

FIG. 16 illustrates a method 160 for testing an IC device that includesa fuse system with one or more soft-blow fuses, such as thoseillustrated in FIGS. 9-12. The method 160 can be implemented by suchsoft-blow fuse systems.

The fuse system receives data defining one or more fuse configurations(step 162). Based on the received fuse configuration data, the fusesystem generates soft-blow signals (step 164), and based on thesoft-blow signals, the fuse system selects an operational state (step166). The selected operational state simulates blown fuses in the fusesystem without permanently blowing those fuses. Thus many different fuseconfiguration can be tested in the same semiconductor device.

Although the present invention and its advantages have been describedwith reference to particular implementations, it should be understoodthat various changes, substitutions, and alterations can be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims. For example, although particular semiconductordevices and device packages have been discussed, the describedtechniques can be used for other devices and device packages; or stepsin the described methods can be performed in different order and stillprovide desirable results. That is, the discussion included in thisapplication is intended to serve as a basic description. It should beunderstood that the specific discussion may not explicitly describe allembodiments possible; many alternatives are implicit. It also may notfully explain the generic nature of the invention and may not explicitlyshow how each feature or element can actually be representative of abroader function or of a great variety of alternative or equivalentelements. Again, these are implicitly included in this disclosure as itwould be understood by a skilled artisan. Where the invention isdescribed in device-oriented terminology, each element of the deviceimplicitly performs a function. Neither the description nor theterminology is intended to limit the scope of the claims.

1. An integrated circuit device packaged in a semiconductor devicepackage, the integrated circuit device comprising: one or more externalterminals configured to receive mode selection signals selecting betweena test mode and a normal mode of operation for the device; one or moreexternal terminals configured in the test mode to receive fuseconfiguration data from an external source; a latch array including aplurality of latches each of which being configured in the test mode toreceive a corresponding data portion of the fuse configuration data andto output a respective soft-blow signal based on the received dataportion; and a fuse array circuit including a plurality of fuses andgenerating a respective output signal for each fuse based on whetherthat fuse is blown or not, wherein each latch in the latch arraycorresponds to a respective fuse in the fuse array circuits, and in thetest mode the fuse array circuit receives the respective soft-blowsignal from each latch and generates the respective output signal forthat fuse based on the received soft-blow signal.
 2. The device of claim1, further comprising: a circuit element receiving one or more of theoutput signals from the fuse array circuit and selecting its operationalstate based on the received output signals.
 3. The device of claim 2,wherein the circuit element includes a voltage regulator providing areference voltage whose value depends on the output signals from thefuse array circuit.
 4. The device of claim 2, wherein the circuitelement includes a delay element configured to receive an input signaland to output a delayed signal following the input signal by a timedelay whose value depends on the output signals from the fuse arraycircuit.
 5. A method for operating a semiconductor device in asemiconductor device package, the method comprising: receiving fuseconfiguration data from an external source; generating a soft-blowsignal based on the received fuse configuration data; receiving thesoft-blow signal in a fuse circuit that includes a fuse and has firstand second operational states corresponding to the fuse being intact andblown, respectively; and selecting the fuse circuit's operational stateto be the first or second operational state based on the receivedsoft-blow signal.
 6. The method of claim 5, further comprising:generating a tune signal in accordance with the fuse circuit'soperational state.
 7. The method of claim 6, further comprising:transmitting the tune signal to a circuit element to tune operationalparameters of that circuit element.
 8. The method of claim 7, whereinthe circuit element includes a voltage regulator or a signal delayelement.
 9. A method for testing semiconductor devices, the methodcomprising: putting a semiconductor device into a test mode, thesemiconductor device including a set of fuses; and testing thesemiconductor device for a plurality of fuse configurations withoutpermanently blowing the fuses, wherein each fuse configurationcorresponds to a respective subset of blown fuses within the set offuses.
 10. The method of claim 9, wherein testing the semiconductordevice for a plurality of fuse configurations includes, for each fuseconfiguration, loading fuse configuration data into a soft-blow circuitof the semiconductor device, wherein the fuse configuration data definesthe respective subset of blown fuses within the set of fuses.
 11. Themethod of claim 9, wherein testing the semiconductor device for aplurality of fuse configurations includes, for each fuse configuration,measuring operational parameters in that fuse configuration.
 12. Themethod of claim 9, further comprising: determining an optimal fuseconfiguration based on the measured operational parameters.